The power amplifier is one of the essential elements in an RF transmission circuit. The power amplifier is configured to amplify signals before they are transmitted. Thus, the power amplifier is usually configured at the front of an antenna transmitter. However, the power amplifier is one of the elements that consume lots of power in the RF transmission circuit. Currently, the power amplifier used in many smart devices (such as, a smart phone, a tablet, and the like) is mainly made of GaAs. Due to the characteristics of having high frequency and insulation, less power consumption, and the weak absorptivity of noises and harmonic waves, GaAs devices can be applied in current 4G signal transmission and may even see application in future 5G signal transmission.